Operation
93
Figure 113Load on bypass (UPS available and battery charging)
3.6.3 Momentary Overloads
An overload in the critical load will continue to be supplied by the UPS system if the overload condi-
tion does not exceed the current versus time curve of overload capacity for the UPS.
For momentary overloads exceeding 200% of rated system current, the static switch turns on for 10
cycles. This provides current from the bypass line in parallel with current from the UPS system out-
put. By providing two power sources simultaneously, high current can be supplied to the critical load
with full output voltage regulation. The critical load can be sustained through inrush currents and
momentary faults.
If an overload situation exceeds 10 cycles, the UPS module continues to supply power to the critical
load if it remains within the current-versus-time curve of overload capacity. If the system overload
capacity is exceeded, the UPS control logic initiates an automatic transfer to the bypass line by oper-
ating the static bypass switch and the contactors (output and bypass).
3.6.4 Input Power Failure (Load on Battery)
If the utility AC power source fails, or is outside the acceptable range, the battery plant becomes the
power source for the UPS module inverter. The UPS system continues to supply power to the critical
load, and also to the UPS controls.
You can use the Battery Time screen at the UPS modules to monitor the present battery voltage com-
pared to the shutdown value. The length of time the battery can sustain the load depends on the size
of the load and the size and condition of the battery plant. The battery plant is typically large enough
to supply a 100% rated load for 15 minutes.
Alarm messages that indicate battery status are Battery Discharge, Low Battery, and Battery Shut-
down. The voltage limits for these alarms are displayed on the UPS module Alarm Limit Settings
screen. These limits were selected for your installation by Liebert Global Services during initial start-
up.
Figure 114Utility fail, load on battery
MIMIC DISPLAY